THE LEAF SPOTS OF THE ELM 

BY 

LEE ELLIS MILES 
A. B. Wabash College, 1914 



THESIS 



Submitted in Partial Fulfillment of the Requirements for the 
Degree of 

DOCTOR OF PHILOSOPHY 

IN BOTANY 



IN 



THE GRADUATE SCHOOL 

OF THE 

UNIVERSITY OF ILLINOIS 
1920 



•& 



to© 



^ 



^' 



LIBRARY OF CONGRESS 
RECEIVED 

AUG12192I 

OOOUMENTS DIVISION 



CONTENTS 

PAGE 

Acknowledgement 160 

I. Introduction 161 

II. The most important American leaf spot 162 

(Gnomonia ulmea (Schw.) Thiim.) 

Distribution and history 162 

Symptoms 165 

Development of stromata 166 

Ascogonium 167 

Further development of perithecium 170 

Asci and ascospores 173 

Expulsion and germination of ascospores 173 

Inoculation with ascospores 176 

Observations on the over-wintering 177 

Conidial stage 1 70 

Glocosporium ulmeum, sp. nov 182 

Inoculations with conidia 183 

III. Another Gloeosporium ON f ekm \ y . '> 184 

Gloeosporium ultnicolum, sp. nov , 185 

IV. Princdpal European leaf spot 1S6 

(Systremma Ulmiy (gchleich.) Thiess. and Syd'.j 

Y. Other leaf spots of elm i8q 

In America 1 80 

List of species occurring in Europe only 192 

Fossil leaf spots of elm 102 

VI. Summary 102 

Literature Cited 104 

Explanation of Plates 195 

Vita 107 



ACKNOWLEDGEMENT 

The writer takes pleasure in making acknowledgement to Dr. F. L. 
Stevens, Professor of Plant Pathology, University of Illinois, for helpful sug- 
gestions and guidance in the preparation of this thesis. The writer also wishes 
to express his appreciation of the valuable assistance given by Professor 
William Trelease, Head of the Department of Botany, University of Illinois, 
in solving questions of a taxonomic nature. Thanks are also due to a number 
of others who have rendered valuable assistance by sending specimens and 
materials for examination and comparison. 



VOLUME LXXI NUMBER 3 



THE 



Botanical Gazette 



MARCH 1921 

LEAF SPOTS OF THE ELM 

L. E. Miles 

(with PLATES VIII-X AND one figure) 

Introduction 

About eighteen species of the genus Ulmus are known (2), 
widely distributed throughout the cold and temperate regions 
of the Northern Hemisphere. Six of these species, U. americana, 
U. fulva, U. racemosa, U. alata, U. serotina, and U. crassifolia, are 
native to America and occur naturally from Labrador to southern 
Mexico. None, however, occur west of the Rocky Mountains. 
U. alata, U. crassifolia, and U. serotina are tender and do not 
grow well in the northern states, but are quite extensively used for 
lawn and avenue trees in the south. U. americana, the most 
widely distributed American species, occurs in practically every 
state east of the Rocky Mountains, and in Canada. It is the 
most characteristic tree of the northeastern states, and is very 
widely used for street planting and as an ornamental tree for lawns. 

Among the fungous enemies of the elm are a number of forms 
which cause leaf spots, the most important of which will be dis- 
cussed in this paper. Ordinarily none of these diseases is of much 
importance economically, but in severe cases they may injure 
the tree materially by causing premature defoliation. This saps 
the vigor of the tree, and if the severe attack is repeated during a 
number of consecutive seasons, may even result in its death, or at 

161 



l62 



BOTANICAL GAZETTE 



[march 



least may weaken it to such an extent that it is not able to with- 
stand the adverse factors in its environment. In a nursery of 
young elm trees these leaf spots may do much more damage than 
when they occur on older trees. 

Most important American leaf spot 

Distribution and history 
Chief among the fungi causing leaf spots of the elm in this 
country is Gnomonia ulmea (Schw.) Thiim. This disease, known 
as the elm leaf spot or elm leaf scab, occurs most commonly on 




Fig. i. — Distribution of Gnomonia ulmea in United States 



U. americana, and is found in greater or less degree throughout 
the entire range of its host. The writer has examined exsiccati 
specimens of it which were collected in New York, Massachusetts, 
Vermont, Maine, New Hampshire, Rhode Island, Connecticut, 
Pennsylvania, Ohio, Michigan, Indiana, Illinois, Wisconsin, North 
Dakota, Iowa, Nebraska, South Dakota, Missouri, Kentucky, 
Tennessee, North Carolina, Georgia, South Carolina, and Texas, as 
well as several from Canada. Text fig. i gives a better idea of its 
wide distribution than does this list of states. It is more than 
probable that it occurs also in the remainder of the states east of 



1921] MILES— LEAF SPOTS OF ELM 163 

the Rocky Mountains, but has not been reported. In addition to 
the normal host, U. americana, specimens have been examined on 
U. fulva, U. alata, U. crassifolia, and U. racemosa, and it is quite 
probable that it may occur also on U. serotina, the only other 
American species. It has not been seen on any European or other 
foreign elm, however, collected either in this country or abroad, 
nor is there any account in literature of its occurrence on such. It 
may be concluded, therefore, that this fungus is strictly an Ameri- 
can species. 

The fungus was first described by Schweinitz (34) as Xyloma 
ulmeum, in 1818, on leaves collected at Aiken, South Carolina. 
His material was immature, and consequently his description was 
incomplete and inadequate. Fig. 7 is a leaf from the type collec- 
tion from which his description was taken. This specimen is one 
of Schweinitz' exsiccati in the Museum of the Academy of Natural 
Sciences at Philadelphia. Comparison of this figure with figs. 3-5, 
showing infected leaves collected by the writer, indicates that the 
fungus with which Schweinitz worked and the one discussed in 
the early part of this paper are identical. 

A few years after Schweinitz' original description, Fries (19) 
described a disease of the American elm as caused by Sphaeria 
ulmea Ft., but gave Xyloma ulmeum Schw. as a synonym, showing 
that he had seen Schweinitz' previous description and recognized 
that he was dealing with the same organism. His description 
added but little to the earlier one of Schweinitz. The next change 
in the taxonomic position of the fungus was made in 1878 by 
von Thumen (39) when he placed it in the genus Gnomonia with- 
out explanatory comment or additional description. In his 
Sylloge Fungorum Saccardo seems to have accepted this change 
with some reservations, since he placed the fungus in the section 
Dubiae of the Sphaeriales, under the name Gnomonia ulmea 
(Schw.) Thiim., without, however, explaining his reasons for 
doing so. 

In 1892 Ellis and Everhart (16) made a further change in 
the name and taxonomic position of the fungus, apparently with- 
out being acquainted with the previous work of von Thumen, 
since they made no mention either of his name or of Gnomonia in 



1 64 BOTANICAL GAZETTE [march 

their account of the synonymy of the organism. They called it 
Dothidella ulmea (Schw.) E. and E., thereby placing it among the 
Dothidiales, although they acknowledge that it is "anomalous on 
account of its ascigerous cells assuming the characters of peri- 
thecia." In 191 5 Thiessen and Sydow (38), in a monograph of 
the Dothidiales, excluded it from that group and referred it back 
again to Gnomonia in the Sphaeriales, where it had previously been 
placed by von Thumen. In addition to these various names, the 
fungus has been much confused by American plant pathologists 
and mycologists with an organism causing a leaf spot of European 
elms in Europe, Systremma Ulmi (Schleich.) Thiess. and Syd. 
(38), to which it has a superficial resemblance, and it has often 
been collected and reported under one or another of various lists 
of synonyms pertaining to that fungus. 

In 1901 and 1902 Stone and Smith (37) from Massachusetts 
reported attempts at controlling the disease by spraying with 
Bordeaux mixture, referring to the fungus as Dothidea Ulmi 
(Duv.) Wint, a synonym of Systremma Ulmi, in the first paper, 
and as Dothidella ulmea, a synonym of Gnomonia ulmea, in the 
second, although they made no reference to the discrepancy. In 
1910 Gtissow (21) reported it from Canada as extending back 
upon the petioles of young shoots to their tips, which twisted 
downward and finally died. He stated that in no case did the 
young shoots so infected recover. In this same year Clinton (8) 
from Connecticut reported that by July or earlier some trees had 
shed almost all their leaves. He stated that these trees later put 
forth a new crop of foliage which was entirely free from the disease, 
but that the other trees, not so severely infected in the beginning, 
showed all their leaves more or less affected, and shed them con- 
tinuously throughout the season. He stated that when defoliation 
was most severe the young branches of the season also had fallen 
off. This latter observation confirms that made by Gtissow in 
Canada. The writer has seldom seen so severe an infection as 
either of these, although in some localities the disease is severe 
enough each year to cause an incessant dropping of leaves through- 
out the summer and fall, which is a far from desirable characteristic 
in a lawn and avenue tree like U. americana. 



iQ2i] MILES— LEAF SPOTS OF ELM 165 

Symptoms 

The disease makes its appearance early in the spring, the 
amount of primary infection apparently being dependent to a con- 
siderable degree on the weather conditions, as it is much worse on 
the same tree in some years than in others. Clinton expressed 
the opinion that the only infection which occurred was the primary 
spring infection, and that there was no further spread during the 
summer. The fact that no conidial or summer stage had ever 
been found connected with the disease, and also his observation of 
trees which shed all their leaves early in the season and which 
later produced a new crop of foliage entirely free from spots, would 
tend to support this conclusion. The absence of the disease on 
the new crop of leaves, however, might have been due to weather 
conditions which were not favorable to the spread of the organism 
at that time. In any case, the writer has found a conidial stage 
constantly associated with the disease in every specimen examined, 
and the connection between the two stages will be clearly shown 
later. Observations show also that the primary infection is con- 
fined almost exclusively to the lowest leaves, and that it is much 
more abundant on the young seedlings, whose leaves are naturally 
closer to the ground, and to the ascospores which are the source of 
this early infection. Moreover, it is only on these young seedlings 
that twig and petiole infection has been observed, although there it 
is often quite severe, killing off the entire new growth. 

The first evidence of the disease is a small whitish or yellowish 
fleck or blotch on the upper side of the leaf shortly after it has 
unfolded. This spot increases in size, and soon a number of small 
black specks begin to appear within the whitened area. As 
these enlarge they sometimes coalesce to form a single, coal black, 
stroma-like, subcuticular structure which is quite irregular in out- 
line and varies from 0.5 to 2 or 3 mm. in diameter. As a rule, 
however, the individual stromata remain separate, when they 
appear to be somewhat concentrically arranged, forming a distinct 
spot, in most cases surrounded by a narrow band of whitish dead 
tissue as shown in fig. 12. Occasionally the black stroma, or the 
group of separate stromata, so closely grouped together as to seem 
to the naked eye to be a single one, may cover the entire discolored 



166 BOTANICAL GAZETTE [march 

area, without a border of whitish or lighter colored dead tissue. 
In this case it appears almost like a tar spot on the normal green 
leaf tissue, and reminds one of some of the species of Rhytisma. 
Later in the season the cuticle which covers the stroma wears 
away and gives the spot an ashen appearance, which is most pro- 
nounced near the edge. These black spots may be so numerous 
as to practically cover the entire upper surface of the leaf. 

In addition to these black stromata, and much more prominent 
in the early stages of infection, although the reverse is the case 
later in the season, are the pustules of the conidial stage. They 
are quite abundant and conspicuous in the early spring, and it is 
hard to understand how they can have been overlooked for so 
long a time. They are subcuticular, irregular in outline, and 
dark, owing to the cuticle which is stained by the fungus, and 
which splits irregularly to allow the dispersal of the spores, which 
are extruded in small white masses. The pustules formed earliest 
seem to have but little or no stromatic base, although those formed 
later in the summer are almost invariably situated on a distinct 
stroma, which they may or may not entirely cover. This conidial 
stage will be discussed more in detail later. 

Development of stromata 

Beneath each one of the small, black, subcuticular stromata, as 
represented in fig. 13, early in its development, beginning about 
the latter part of May, there commences the development of the 
young perithecium of the causative fungus. The stroma now 
becomes somewhat looser in structure near its central region, 
beneath which the perithecium is to be formed. The normal cells 
of which the stromatic hyphae are made up are short, approxi- 
mately isodiametrical (fig. 16), and contain comparatively little 
protoplasm, which little soon disappears, except in the basal layer 
of cells, and in those which are actively engaged in extending the 
edges of the stroma. They are more or less olivaceous to dilute 
brown in color, the depth of the hue depending on the age of the 
cell, but the very dark appearance of the stroma is due principally 
to a dark coloring matter which is not present in the cell wall to 
any extent, but seems to be excreted by the cells of the fungus 



i 9 2i] MILES— LEAF SPOTS OF ELM 167 

and deposited between their walls. A similar excretion of coloring 
matter was noted by Klebahn (22) in working with Gnomonia 
veneta (Sacc. and Speg.) Kleb. Within the looser portion of the 
stroma are to be found in this stage of its development other 
hyphae, which are very thin-walled, entirely filled with a very 
dense protoplasm, and have comparatively few septa. They 
stain pink or red with Pianeze Illb stain (41), as do the other 
hyphae which enter into the formation of the young perithecium, 
but much more intensely. The ordinary stromatic elements, 
which have become comparatively inactive, take a green color 
with this stain. These deeply staining active hyphae ramify 
through the lower, looser portion of the stroma, a number of them 
turning upward near the center and breaking through to the out- 
side, extending above the leaf surface as shown in fig. 16. 

Ascogonium 

Immediately beneath this portion of the stroma there grows 
downward into the leaf tissue, between the epidermal cells and 
between the cells of the upper palisade tier (usually to a point near 
the lower edge of that layer), one of these hyphae which has become 
slightly larger in diameter. For convenience this hypha may be 
termed an "infection thread" or "suspensor," since it is the first 
of the fungal hyphae to invade the tissue of the host beneath the 
epidermal layer, and since in the early stages of its development 
the young perithecium gives the appearance of being suspended 
from the subcuticular stroma above by means of it. This hypha 
is accompanied in its growth downward into the host tissue by a 
number of other hyphae, consisting of short isodiametrical cells, 
which arise from the basal layers of the stroma and contain com- 
paratively little protoplasm. They form a sheath for the broader, 
more deeply staining hypha, which for convenience only has been 
designated as an infection thread or suspensor. After growing to 
a point about midway down in the palisade layer, this cuts off a 
number of cells at its extreme end (fig. 16), usually three or four, 
which coil somewhat in the form of a spiral. Each one of these 
cells contains two or more nuclei, while the cells of the hyphae 
which constitute the sheath are uninucleate. These hyphae 



168 BOTANICAL GAZETTE [march 

meanwhile have continued their growth, dividing in such a manner 
as to produce a larger number of chains of cells which arrange 
themselves spirally about the central coil and form what is to 
become the wall of the perithecium. 

This coiled structure is the ascogonium or "Woronin's hypha," 
described by various workers in a considerable number of Ascomy- 
cetes. I do not consider the hypha connecting it with the stroma 
above in any way analogous to a trichogyne, however, but rather 
as being similar to and corresponding to the hypha described by 
Miss Dawson (14) as leading from the stroma beneath and giving 
rise to "Woronin's hypha" in Poronia punctata. The apparent 
differences between the two cases are that in Poronia the peri- 
thecium is formed in the upper part of the stroma, and the hypha 
which gives rise to the ascogonial coil comes up from below and 
does not leave the stroma; while in Gnomonia ulmea the peri- 
thecium is formed beneath the stroma in the tissue of the host, 
which renders it necessary for the thread which is to give rise to 
the ascogonium to leave the stroma and grow downward into the 
leaf tissue. In each case the hypha enters the perithecial primor- 
dium at a point which is finally located in the basal portion of the 
mature perithecium. In Poronia, however, after coiling to form 
the ascogonium, it continues to grow on beyond the perithecium 
to the outer surface of the stroma as a somewhat narrower thread, 
which reminds one of the trichogyne of Collema, as described by 
Bachman (3), of Physcia by Darbishire (ii), and of Polystigma 
by Frank (18) and Fisch (17), but not by Blackman and Wells- 
ford (4). This " trichogyne" was not present in Gnomonia ulmea. 

Brooks (6), in working with Gnomonia erythrostroma (Auers.) 
Kleb., found an ascogonium similar to the one described for 
G. ulmea, and also certain structures which he called trichogynes. 
He was able to trace a connection between these hyphae and the 
peripheral layers of the young perithecium only, never with the 
ascogonium itself. These peripheral layers would correspond in 
fig. 16 to the sheathing hyphae a. Since more than one trichogyne 
passed through a single stoma in the case in which he was working, 
Brooks concluded that more than one series of trichogynes was 



iQ2i] MILES— LEAF SPOTS OF ELM 169 

connected with a single ascogonial coil. In G. ulmea also, as 
previously stated, one finds (fig. 16) certain hyphae which pass out 
through the upper leaf surface in a quite similar manner, although 
not through a stoma in this case, since stomata are absent on the 
upper surface of an elm leaf. In this case, however, there is no 
possibility of their being mistaken for anything else than vegeta- 
tive hyphae. It is quite likely that those of G. erythrostroma are 
of a similar nature. Blackman and Wellsford described in 
Polystigma rubrum trichogynes similar to those of Brooks, but on 
account of an inability to trace a direct connection with the asco- 
gonium, concluded that they were merely vegetative. In earlier 
papers Fisch (17) and Frank (18) had both described and fig- 
ured such connections and had designated the hyphae as true 
trichogynes. Although Brooks continued to call the projecting 
hyphae in G. erythrostroma trichogynes, and although he found 
both ascogonia and spermatia present, he concluded that the 
trichogynes were no longer functional, and that fertilization did not 
actually occur through their agency. He suggested as a present 
function for them that they might serve as respiratory channels 
for the fungal hyphae within the leaf, where the assimilatory pro- 
cesses must necessarily have been considerably curtailed by the 
dying of the tissue. Such a function would also give reason for 
the existence of similar hyphae in G. ulmea, especially since the 
presence of the black stroma would tend even more to impair the 
respiratory processes in the host tissue beneath it. 

The ascogonium in the young perithecium of G. ulmea soon 
begins to break up into segments, each cell becoming separated 
from the others. Brown (7) noticed a similar segmentation of 
the ascogonium of Xylaria tentaculata, as did also Miss Dawson 
in Poronia. They found that those segments gave rise to the 
ascogenous hyphae in the fungi with which they were working, 
but I have been unable to ascertain this fact with certainty in 
G. ulmea with the material at hand. It is almost a certainty, 
however, that this is the case here also, since the segments of the 
ascogonial coil can be distinguished near the base of the perithe- 
cium until after the asci have commenced their development. 



170 BOTANICAL GAZETTE [march 

Further development of perithecium 
In the further development of the young perithecium all sign 
of the connection with the subcutaneous stroma soon disappears, 
as is shown in fig. 2, which is a slightly older stage. The structure 
has increased in size, chiefly by the enlargement of the portion 
which is later to become the perithecial cavity, but which is now 
filled with a dense pseudoparenchyma. The wall has also increased 
somewhat in thickness by the formation of new layers on the 
inside. As yet there is no sign of a beak or ostiole, although the 
wall cells on the lower side of the perithecium, opposite the stroma, 
are somewhat denser in protoplasmic contents, as is shown by the 
slightly darker color. Fig. 8 shows a still later stage of develop- 
ment in which the perithecium has practically doubled in size, 
since the two figures are of the same degree of enlargement. The 
central area has enlarged and the wall become still thicker. The 
darkly stained portion is composed of young asci which are not 
yet clearly differentiated. On account of the nature of the material, 
the leaves showing this stage of development having first been 
collected and dried and later softened with lactophenol, as well as 
on account of the very small size of the nuclei, the cytological and 
other minute details of this development could not be accurately 
determined. The main portion of the perithecial cavity is entirely 
filled with a very fine pseudoparenchymatous material, which 
when crushed or teased out appears merely granular in structure, 
with some slight evidence of anastomosing hyphae. In the origi- 
nal description of the fungus, Schweinitz mentions the granular 
nature of the perithecial contents. The beak or rostrum and the 
ostiole are here seen in the earliest stages of their development. 
The same group of more deeply staining wall cells, mentioned in 
connection with fig. 2, is still evident, but has increased in size to 
form a sort of plug of tissue, which by its growth forces the outer 
layers of the perithecial wall outward and downward on the lower 
side to form the outer wall of the beak. As the multiplication of 
these actively dividing cells continues, their long axis changes 
from horizontal, as at first, to a direction parallel to that in which 
the beak is being developed. The cells nearest the center of this 
elongating beak separate in their continued growth, leaving a 



1921] MILES— LEAF SPOTS OF ELM 171 

channel throughout its entire length which becomes the ostiole. 
This channel is lined with periphyses or hairlike structures which 
are hyphal outgrowths of the inner or lining layer of cells. These 
periphyses all point in a direction outward from the perithecial 
cavity, and so form a one-way passage from the spore bearing 
portion to the outside of the leaf. As the development of the 
beak nears completion, each layer of cells, whose increase has 
brought about its elongation, produces at its lower end one or 
more of these periphyses to each cell, so that the lower end or 
outer opening of the ostiole is surrounded by a considerable brush 
of them. These later stages of the development of the ostiole are 
seen In fig. 1, which shows two perithecia in an almost mature 
condition. The beaks are slightly longer than normal at this 
stage of maturity, but in all other respects the perithecia are 
typical. No further elongation of the beaks occurs until the 
ascospores are fully mature and ready to be discharged, sometime 
in the early spring, at which time they again begin growth and 
continue until they have just broken through the lower epidermis. 
In this stage, which is the condition in which they pass the winter, 
the lower end of the beak is still within the leaf tissue and merely 
pushes out the lower epidermis in the form of a hump or tubercle. 
In the spring, when they have just broken through, these beaks, 
although short, are quite conspicuous on account of their fresh 
dark brown or almost black color. 

The asci in the figure last referred to are not yet mature, and 
it will be seen that the pseudoparenchyma is still present. This 
tissue is composed of small hyaline cells, filled with a very dense 
granular protoplasm, and with very thin walls; in fact, the walls 
are little more than membranes. It occupies the entire central 
region before the development of the asci, which grow out into it, 
and apparently it is used up by the asci in their growth, as no 
crowding of the tissue is apparent ahead of them. Such an inter- 
ascicular pseudoparenchyma has been described by Stevens (35), 
who used it as the basis for the formation of a new genus, Desmotas- 
cus. He considered it an instance of delayed dissolution of the 
pseudoparenchymatous central region of the developing peri- 
thecium to form the central cavity, and suggested that, since this 



172 BOTANICAL GAZETTE [march 

structure was not clearly seen without good thin microtome 
sections, the same thing may exist in other perithecia and have 
been overlooked because the microtome was not used. The find- 
ing of such a structure in Gnomonia ulmea would tend to support 
such a hypothesis. Reddick (29), working with Guignardia 
bidwellii, found that when the first asci were developing not nearly 
all the pseudoparenchyma was gone, and that, when crowded 
together by the growth and expansion of two asci, it gave the 
impression that paraphyses were present. He also expressed the 
opinion that these cells were absorbed by the growing asci. This 
case differs from that found in Gnomonia ulmea and also from that 
described by Stevens in Desmotascus only in that the pseudo- 
parenchymatous cells in the latter two fungi never appear to be 
crowded by the invasion of the asci. 

The asci originate from the basal portion of the perithecial 
cavity, and also from the sides to a point about halfway to the 
top. The perithecial walls are composed of from 10 to 12 rows of 
cells (fig. 1), the outer one or two layers of which have assumed a 
bright golden brown color. It is at about the time when the ostiole 
is being developed that this coloration of the wall begins. Until 
that time the wall has been entirely hyaline. From this time on, 
as the perithecia age, this color becomes constantly darker, until 
about midwinter, when it is almost black. The outer surface of 
the perithecium is smooth, and there are no loose hyphae connect- 
ing it with the leaf tissue in which it is borne. 

When mature the perithecia are nearly spherical or usually 
somewhat wider than deep. They vary considerably in size, but 
average about 250-300 fx in diameter and 150-200 jx in depth. 
The ostiole is usually about 100 /j, long and 75 fx wide, but may 
reach a considerably greater length. The size of the perithecium 
is so great that the upper epidermis is elevated in the form of small 
tubercles, and the beaks push out the lower epidermis in the same 
manner, before they break through it. They do not extend any 
distance beyond the outer surface of the lower epidermis, as do so 
many of the species of Gnomonia, but merely reach through it. 
When the over-wintered leaves have been soaked in water, the 
perithecia may be picked out with the point of a sharp scalpel, and 



iQ2i] MILES— LEAF SPOTS OF ELM 173 

on account of the absence of any hyphae connecting them with 
the leaf tissue, they leave a smooth cavity or locule in the leaf. 

ASCI AND ASCOSPORES 

In mature perithecia the asci are very much confused in their 
arrangement, owing to the fact that the older ones are broken 
loose from their attachment and pushed toward the top of the 
perithecial cavity by the younger ones. There are no paraphyses. 
The asci are oblong-cylindrical or somewhat club-shaped in form, 
and have a short stalk at the base- which may be either straight 
or bent toward one side. The wall is hyaline, thin below, but 
thickened in the upper half (fig. 19), and does not color with 
iodine. At the upper end of the ascus is a pore surrounded by a 
ring of thickened tissue which is strongly refractive toward light. 
In optical section as seen from the side this ring presents the 
appearance of two small spheres arranged side by side in the apex 
of the ascus. The asci measure 45-55 X9-11 M- The spores are 
very characteristic also. They are hyaline, elongate-elliptical, or 
obovate-oblong, and have a septum near the lower end, thus 
becoming unequally two-celled. They are eight in number, sub- 
biseriate, and measure 8-10X3-3 -5 M- The small cell at the 
lower end of the spore averages about 2 /j, both in length and 
breadth. There is a slight constriction at the septum. Some 
epiplasm is present in the mature ascus along with the spores. 

Expulsion and germination of ascospores 
As previously stated, the asci in a mature perithecium become 
loosened from their attachment at the base and crowded toward 
the apex of the perithecial cavity in a somewhat disordered mass. 
In the process of expulsion of ascospores an entire ascus enters the 
lower part of the ostiole and is held in place by the periphyses 
until the pressure produced by the absorption of water, which 
must be present to allow the ascospores to be discharged, becomes 
sufficient to bring about the discharge of the spores. These pass 
outward through the periphysis-lined ostiolar channel to the sur- 
face of the ostiole, where they are expelled with some force, and 
under natural conditions are evidently dispersed by currents of 
air. Early in March leaves were found which had passed the 



174 BOTANICAL GAZETTE [march 

winter in the open under natural conditions, on which occurred 
perithecia in such a stage of development as to expel ascospores 
within two days after being brought into the laboratory. It was 
found that spore expulsion was very slow and limited or did not 
occur at all when the leaves were kept too moist or when main- 
tained in a saturated atmosphere, such as occurs when they are 
placed on moistened filter or blotting paper in a closed Petri dish. 
When the lid of the dish is removed, however, and the leaves are 
alternately allowed to become dry and again moistened by adding 
water to the filter paper beneath them, the spores are expelled in 
considerable quantities. If they are then caught on a glass slide, 
either dry or coated with a thin film of egg albumin, glycerine, or 
some such adhesive, it is found that the spores are deposited in 
clusters or groups of eight. Later, as a very large number of 
spores are discharged from a single ostiole, this grouping of course 
is not apparent. The best method for catching the expelled spores 
was that used by Anderson and Rankin (i) in working with 
Endothia parasitica, as described previously. The glass slide was 
suspended by means of match sticks fastened to it near the ends, 
thus bringing it 3 or 4 mm. above the opening of the ostiole. 

Klebahn (27) has shown that this method of spore expulsion is 
general to Gnomonia and to many other fungi which have Gnomonia- 
like, beaked ostioles. The expulsion of the asci into the neck of 
the ostiole appears largely due to the swelling pressure of the ascus. 
When dry, the ascus with its contained spores occupies considerably 
smaller space than after it has been moistened with water. Many 
workers have maintained that ascospores are ordinarily liberated 
one at a time, and such may be the case here, since I have been 
unable to observe the actual act of expulsion of the spores from 
the ascus, but the clusters of the spores intercepted on a glass 
slide suspended above the opening of the ostiole are always in 
groups of eight, and give the impression of having been expelled 
in a group, as was found by Anderson and Rankin to occur in 
Endothia parasitica. 

Many attempts have been made to germinate the ascospores of 
Gnomonia ulmea under various conditions, and on a number of 
different nutrient media, ranging from distilled water, tap water, 



i 9 2i] MILES—LEAF SPOTS OF ELM 175 

extract of dried elm leaves, and sugar solutions, to solid media 
such as the agars of cornmeal, bean, potato, Brazil nut, onion, 
elm leaf, and plain washed agar. In distilled or tap water the 
spores swelled considerably, especially the larger cell, and some- 
times a spore would give the appearance of being on the point of 
sending out a germ tube from the side of the larger cell, but this 
never occurred. This is in accordance with the results obtained 
by Klebahn (27) in Gnomonia alniella and Gnomoniella tubiformis, 
which he was not able to grow in culture, but is contrary to his 
results with Gnomonia platani and G. leptostyla, both of which 
grew well on nutrient media, the latter even producing the peri- 
thecial stage in such cultures. It would seem that the ascospores 
of Gnomonia ulmea, as in G. alniella and Gnomoniella tubiformis, 
require the stimulation given by the green leaf of the host plant 
itself in order to induce germination. Wolf (42) found that this 
was the case in Diplocarpon rosae, the ascospores of which would 
not even germinate in a drop of water in which a portion of a 
green leaf of the host had been placed, but must be placed in a 
drop of water directly on the living leaf itself. This assumption 
was later confirmed by experimentation. Toward the middle of 
March a number of twigs were cut from an elm and placed in the 
greenhouse with their cut ends immersed in water. In about 
three weeks the buds on these twigs unfolded. A number of the 
young leaves were removed and placed in a moist chamber with 
their surfaces in contact with a slide on which a large number of 
the expelled spores of Gnomonia ulmea had been intercepted as 
previously described. Intimate contact was secured by moistening 
the surface of the slide to which the spores adhered with a drop 
of water. By removing the leaf it was possible to examine the 
spores on the slide by means of a microscope, but never was one 
of them found to have germinated. Later, when the leaves on the 
trees outside the greenhouse had begun to unfold, the same experi- 
ment was attempted again, and in twelve hours it was found that 
a considerable number of the spores in contact with the leaves 
had germinated. This led to an examination of the tree from 
which the leaves used in the first experiment had been obtained, 
and it was ascertained to be an English elm, Ulmus campestris. 



I7 6 BOTANICAL GAZETTE [march 

This led to a further attempt to germinate the spores on the leaves 
of both the English and the Scotch elm, U. glabra, but without 
success in either case. A considerable percentage of germination, 
however, was always obtained with U. americana. These experi- 
ments would seem to indicate that the germination of the asco- 
spores of Gnomonia ulmea is dependent on a special stimulus of 
some sort exerted by the leaves of susceptible species of Ulmus, but 
which is absent in the leaves of other species of the same genus, 
just as it is absent in tap or distilled water, and the various liquid 
and solid nutrient media in which attempts were made to grow 
the fungus. 

At the end of twelve hours of contact with the leaf of the 
American elm under suitable moisture conditions, as previously 
stated, the spores were found in various stages of germination. 
Wherever two spores lay in contact with each other and also with 
the leaf, there was noted a brown coloring matter deposited between 
them. This coloring matter is similar to that previously mentioned 
as being deposited between the hyphae of the stroma and on the lower 
side of the cuticle. The germ tube usually arises from the large 
cell of the spore only, as shown by fig. 20, although in a very few 
instances the small cell also may send out one. Germination 
apparently can occur from any point in the spore, although usually 
the germ tube makes its exit from the side of the large cell. One 
can tell where the germ tube is going to form even before any 
swelling occurs by the excretion of the brown coloring matter on 
the outside of the spore wall at that point. As the tube grows, 
the coloring substance is deposited along its entire length, except 
at the extreme apex, but in considerably greater density at the 
point where it leaves the spore. The substance is present in 
greater abundance also wherever two germ tubes touch or cross 
each other. 

Inoculation with ascospores 

On April 6 a number of abscissed twigs of Ulmus campestris, 
whose leaves had unfolded in the greenhouse, were inoculated 
with the ascopores of Gnomonia ulmea. Twelve twigs were used, 
six being sprayed by means of an atomizer with a suspension of 
spores, while six similar ones were sprayed with sterile distilled 



iQ2i] MILES— LEAF SPOTS OF ELM 177 

water to serve as checks. Each set was kept under a bell jar, 
whose inner surface had been lined with moist filter paper, for a 
period of 42 hours, after which they were left in the normal atmos- 
phere of the greenhouse. A like number of twigs of U. americana, 
whose leaves had unfolded normally outside the greenhouse, were 
treated in a similar manner. As was to be expected from the 
failure to secure germination of the ascospores on the leaves of the 
English elm, no infection occurred on that host. On April 25, 
however, or after a period of about three weeks, eight leaves of the 
American elm were found to bear well defined spots quite charac- 
teristic of the early stages of Gnomonia ulmea. Two of these 
leaves bore three spots each, another one two, and the other six 
had only a single one on each. These spots showed well developed 
pustules of the conidial stage, which is to be described later. In 
addition to these well defined spots a number of leaves showed 
small whitish flecks or blotches, thereby indicating that if the 
experiment had been allowed to continue for a longer period the 
percentage of infection would have been higher. 

Observations on over- wintering 

A number of observations have been made on the over-wintering 
of the fungus on elm leaves under various conditions, and some 
attempts have been made to hasten its development by placing 
the leaves under various controlled conditions. Leaves on which 
the spots occurred were brought into the laboratory, both before 
and after they had been severely frosted, and some were immersed 
in water, both at room temperature and in the refrigerator. Others 
were placed in a moist chamber suspended over water, both in the 
laboratory and refrigerator, and others were placed in each of 
these places under their normal conditions of humidity. Still 
others were suspended over calcium chloride in each of these 
temperatures in order to assure a dry atmosphere. It was found 
that no further development occurred in the leaves which were 
immersed in water, and that the fungus soon died, the perithecia 
becoming mere empty husks. This was confirmed by comparison 
with leaves which had wintered normally outside the laboratory. 
On leaves which had been buried slightly in the soil or were in close 



178 BOTANICAL GAZETTE [march 

contact with the soil underneath a layer of other leaves, the peri- 
thecia were found in early spring to be in approximately the same 
condition. No further development of the fungus occurred on 
the leaves either suspended above the calcium chloride or in the 
normal humidity conditions of the laboratory or of the refrigerator. 
The fungus in the leaves which had been suspended above water 
in a moist chamber, however, did continue its development, and 
by midwinter a few perithecia were found in which the spores 
were apparently practically mature. In most, and finally in all 
cases, however, numerous saprophytes developed in such abundance 
that the Gnomonia fungus was overgrown and destroyed before 
the spores could mature. Other leaves from outdoors were brought 
into the laboratory at various times throughout the winter and 
placed in moist chambers, but the same development of extraneous 
saprophytes soon stopped the observations. In a number of 
instances observed the Gnomonia, apparently in an effort to 
counteract and overcome the encroachments of the more rapidly 
developing saprophytic fungi, began to grow vegetatively, and the 
entire perithecial cavity as well as the ostiolar canal became filled 
with a mass of interlaced and anastomosed hyphae, so compacted 
together that under pressure the perithecial wall would break 
away, but the interior mass would tend to retain its spherical 
shape. This tissue later died and disintegrated, however, leaving 
the empty husk of the perithecium. Among the saprophytes 
which hindered observations a number of forms were invariably 
present. They were, in the main, Cephalothecium roseum, Phy- 
comyces nitens, several species of Penicillium and Aspergillus, an 
Alternaria, a Pleospora, a Crytostyctis, and a Myxomycete. 

Various observations also were made on leaves wintered out- 
side the laboratory. Some leaves were placed on shelves of a 
wire cage, others were placed on the ground and covered with other 
leaves and soil, while still others were wrapped in cheesecloth and 
placed on the surface of the ground. In the leaves placed on the 
shelves and on the surface of the ground the fungus was found to 
mature more rapidly than on those leaves covered with other leaves 
and soil, and a very few perithecia were found on such, which 



iQ2i] MILES— LEAF SPOTS OF ELM 179 

contained some spores apparently almost mature as early as the 
middle of February. On only one leaf, however, were any of the 
perithecia at that time mature enough to expel spores. This leaf 
was on the shelf of the wire cage, which was placed directly against 
the south wall of the greenhouse, and was exposed both to the 
direct rays of the sun and also to the heat rays radiated from the 
cement wall. In most cases at that time the asci were somewhat 
more developed than when observed in the fall, but the spores 
were not yet differentiated. The normal development during the 
winter, therefore, seemed to be very slow. In leaves which were 
in especially damp situations, as those buried in the soil or those 
in intimate contact with the soil under a cover of other leaves, 
most of the perithecia were found to be dead and disintegrated. 
In general, it seemed that leaves neither in too exposed nor too 
moist a situation, as for instance those toward the middle of a 
pile of leaves, showed the greatest development of the fungus late 
in winter and early in the spring. 

CONIDIAL STAGE 

In every specimen examined in which the ascigerous stage of 
Gnomonia ulmea occurred, I have found constantly associated 
with it an imperfect or conidial form. This stage was found present 
from early spring until late fall on every leaf collected, and also 
on all exsiccati material examined, even the Schweinitzian type 
specimen previously mentioned. I have examined all available 
published exsiccati specimens of Gnomonia ulmea, as well as more 
than 100 other specimens obtained for purposes of comparison 
from various educational institutions and private individuals, 
including several from the Royal Botanical Gardens, Kew, England, 
and the herbarium of the University of Geneva, Geneva, Swit- 
zerland. The published exsiccati specimens examined are as 
follows: Ravenel Fung. Amer. Exsic. no. 752; Ravenel Fung. 
Carol., Fasc. II, no. 63; Ellis and Everhart Fung. Col. nos. 239, 
2928, and 3422; Seymour and Earle Econ. Fung. nos. 155a and 
155b; Ellis N. Am. Fung. no. 1347; Brenckle Fung. Dakotensis 
no. 329; Rabenhorst-Winter Fung. Eur. nos. 3661a and 3661b; 
and von Thumen Myc. Univ. no. 1155. 



180 BOTANICAL GAZETTE [march 

The conidial layer develops on the stroma which is found on 
the upper surface of the leaf above the base of the young perithecium 
(fig. 14). It may cover only a portion of the stroma, and there 
may be two or even more of them on a single one of the stromata. 
Again, a stroma may develop, to all appearances identical with 
those formed above the bases of the young perithecia, but the 
perithecium be lacking. In this case the conidial pustule invariably 
covers the entire surface of the stroma. Moreover, in the case of 
the first pustules formed in the spring, there is usually little or no 
stromatic base present. 

The conidial pustules are quite irregular in outline (fig. 18), 
although usually approaching a somewhat circular shape. Unless 
two or more of them coalesce, which frequently, in fact usually, 
happens, they may become considerably elongated and variously 
lobed. The size also varies to a considerable extent, due to the 
coalescing of a number of different pustules. The average size is 
about o . 5 mm. in diameter, although they may be considerably 
smaller, and have been seen as large as o . 8 mm. The upper layers 
of cells of the subcuticular stroma elongate in a direction at right 
angles to the surface of the leaf and form the conidiophores. These 
press closely against the cuticle and lift it up somewhat in the 
course of their development. At the same time they give off a 
brown coloring matter which is deposited on the inner or lower side 
of the cuticle, which itself remains colorless. This coloring sub- 
stance is deposited more deeply at the points between the conidio- 
phores than directly above them, so that the darkened cuticle 
presents a somewhat reticulate or netted marking, and on casual 
observation appears to be composed of fungal tissue. This gives 
the impression that the conidial pustule is of the nature of a di- 
midiate pycnidium. Closer observation, however, shows that no 
fungal hyphae enter into this covering layer, and the structure 
consequently is found to be melanconiaceous in character. The 
deposition of coloring matter on the cuticular coverings of such 
acervuli has been noted by Klebahn in connection with the conidial 
stages of Gnomonia padicola (23), G. leptostroma (22), and Gnomoni- 
ella tubiformis (24). As previously stated, the same substance is 
deposited between the cells of the hyphae which make up the 



i92i] MILES— LEAF SPOTS OF ELM 181 

stroma, and which now have become the cells of the hymenial 
layer from which the conidiophores arise. It is also frequently 
found deposited between the cells of the epidermis immediately 
beneath the stroma. 

These epidermal cells are not changed to any considerable 
extent except for crystalline substances occasionally found deposited 
in them. The fungal hyphae grow down between them and 
crowd them apart somewhat, but they do not lose their arrange- 
ment as a definite layer. The hyphae of the fungus do not pene- 
trate the cells of the host. The conidiophores are crowded together 
into a very compact layer, and are 8-12 fj. long by 1 . 5-2 . 5 jx thick. 
They are without septa, except for an occasional one near the base, 
and terminate in a threadlike projection on which the spores are 
borne. The conidia are elongate-oblong or cylindric, bacillar, 
pointed at one or both ends, straight or sometimes slightly curved, 
one-celled, hyaline, and measure 5-6X1-1.5^ (fig- 15) in a dry 
state, but 8-10X2-2 .5 \x when freshly collected. 

Since there is no fungal covering to the conidial layer, the 
fungus falls into the family Melanconiaceae, and its other charac- 
ters indicate beyond a doubt that it is a member of the genus 
Gloeosporium. It seems to be quite characteristic of Gnomonia to 
have a conidial stage which is melanconiaceous in character. 
Gnomonia padicola has as an imperfect stage Aster oma Padi, but 
according to Klebahn (26) no true pycnidium is formed. Gloeo- 
sporium nervisequum is connected with Gnomonia veneta, Mars- 
sonina Juglandis with G. leptostyla, Gloeosporium quercinum with 
G. quercina, Gloeosporium Garyae with C. Caryae, Gloeosporium 
Tiliae with G. Tiliae, and Leptothyrium alneum with Gnomoniella 
tubiformis. Klebahn (25) has shown also in connection with 
Leptothyrium alneum that no true pycnidial covering is formed, 
and that consequently it is melanconiaceous in structure. Sac- 
caedo (30) also remarks concerning this species " (perithecio) 
subinde tamen spurio et ex epidermide mutata et atrata formato." 

The genus Gnomonia contains a number of species which form 
no conidial stage, or at least whose conidial stage has not yet 
been discovered. In so far, however, as the conidial stages have 
been established in the genus, it is evident that they conform to a 



182 BOTANICAL GAZETTE [march 

more or less close resemblance to Gloeosporium. The Leptothyrium 
of Gnomoniella tubiformis is scarcely to be distinguished from a 
Gloeosporium; Aster oma of Gnomonia padicola differs from it 
only in the production of superficial mycelium; and Marssonina 
of Gnomonia leptostyla only in its two-celled conidia. 

Among the many fungous diseases occurring on the leaves of 
the elm, only a few have been found whose causative organisms 
are located in the Melanconiaceae. Three of these belong to the 
American flora, namely, Goryneum tumoricolum Peck, Septogloeum 
profusum (Ell. and Ev.) Sacc, and Cylindrosporium ulmicolum 
Ell. and Ev. I have not seen Ellis and Everhart's specimen of 
Cylindrosporium ulmicolum, and it may be identical with Phleo- 
spora JJlmi (Fr.) Wallr., since the two descriptions appear very 
much alike. Septogloeum profusum has been reported as occurring 
on the leaves of Ulmus alata and U. americana, although it was 
originally described on Corylus americana. Two species of Gloeo- 
sporium, or rather one species and a variety of the same, have 
been described on the elm in Europe. One of these, Gloeosporium 
inconspicuum Cav., was described on Ulmus americana in Italy, 
but has never been reported in this country. It was distributed 
by Briosi and Cavara in "Funghi parassiti" as no. 350. It 
causes large ochraceous spots on the upper side of the leaf, and 
has very small bacteriform spores, only 1-2 \x in length. A variety 
of this species, Gloeosporium inconspicuum Cav. var. campestris 
Dor. (15), has been described on Ulmus campestris in Russia. 
From the description this is quite similar in external appearance 
to the preceding species, but the spores and conidiophores are 
considerably larger, the spores measuring 3-6 (sometimes 9) X 1-2 ^u. 
The fungus described as occurring on Ulmus americana and other 
species of elm in America in connection with Gnomonia ulmea does 
not agree in any particular with any of these, and therefore I pro- 
pose for it the name Gloeosporium ulmeum, with the following 
formal description. 

Gloeosporium ulmeum, sp. nov. — Acervuli somewhat gregari- 
ous, often confluent, borne on black stromata, usually over the 
base of the developing perithecium of Gnomonia ulmea, covered 
by the darkened cuticle, which later splits and cracks irregularly 



192 1] MILES— LEAF SPOTS OF ELM 183 

and finally breaks away entirely, subrotund or irregular, averaging 
500 fx in diameter, but often as large as 800 ju, epiphyllous, very 
rarely hypophyllous ; conidiophores cylindrical, crowded, occasion- 
ally with a septum near the base, 8-1 2X1. 5-2 n, terminating in a 
threadlike projection on which the spores are borne; conidia 
elongate-oblong or cylindric, bacillar, pointed at one or both ends, 
straight or very slightly curved, hyaline, one-celled, 5-6 X 1-1 . 5 /jl 
in a dry condition or 8-10X2-2.5 fj. when freshly collected, and 
extruded in small white masses. 

Habitat on the living leaves of Ulmus americana, U. fulva, U. alaia, 
U. racetnosa, and U . crassifolia. Common. Conidial stage of Gnomonia 
ulmea (Schw.) Thiim. and constantly associated with it, the two stages occurring 
concurrently on the same leaf and spot. Type specimen on U. americana. 
collected at Urbana, Illinois, August 1919, and deposited in the herbarium 
of the University of Illinois. Differs from Gloeosporium inconspicuum Cav. 
in the very different appearance of the spots and in the larger size of its spores, 
and from Gloeosporium inconspicuum Cav. var. campestris Dor. in the charac- 
ter of the spots. 

Inoculations with conidia 
On April 25 a number of leaves of the American elm were 
placed in a moist chamber lined with filter paper, and at a definite 
point on each was placed a drop of distilled water containing a 
considerable number of spores of Gloeosporium ulmeum, the conidial 
stage of Gnomonia ulmea. On June 2 most of these spots were 
lighter in color than the remainder of the leaf, and on June 5 a 
few of them showed distinct conidial pustules entirely character- 
istic of the fungus with which the leaf had been inoculated. On 
the same day on which this experiment was started a number of 
leaves of a seedling elm, quite healthy in appearance and growing 
naturally in the open, were sprayed with a suspension of the same 
spores in distilled water by means of an atomizer, and the entire 
twig was inserted into an Ehrlenmeyer flask. The mouth of the 
flask was closed by means of a split cork in which a channel had 
been hollowed to fit about the twig. The flask was supported by 
means of props in such a manner that the twig remained in its 
proper position. On June 5 the entire new growth of the twig 
was found to be covered with a practically continuous layer of 
pustules of Gloeosporium ulmeum, all of which were extruding 



184 BOTANICAL GAZETTE [march 

spores copiously. Not only were the leaves badly infected, but 
also the petioles and the stem itself. 

These experiments, together with the production of the conidial 
stage on the leaves of the American elm inoculated with the 
ascospores of Cnomonia ulmea, prove conclusively that the two 
forms are merely stages of the same fungus. The enormous num- 
ber of spores produced by the conidial stage, as well as the fact 
that infection secured from inoculations with such spores was 
much more pronounced and occurred in a somewhat shorter period 
of time than from inoculation with ascospores, would seem to 
indicate that the Cloeosporium stage is the chief agency through 
which widespread dissemination occurs in the spring and early 
summer. 

Another Gloeosporium on elm 

While working with this fungus, a single tree in a nursery at 
Oconomowoc, Wisconsin, was found on which the leaf spots were 
quite different in external appearance from those on the surround- 
ing trees, most of which were abundantly spotted with the Gnomonia 
disease, although the trees were of the same species and had appar- 
ently been planted at the same time. Fig. 9 shows a leaf from 
this collection. The leaf spot is raised considerably more than is 
the case in the preceding species, giving the portion of the leaf on 
which it occurs a crumpled appearance where the spot becomes 
large, and is confined quite closely to the leaf veins, along which 
it spreads, often extending the entire distance from the midrib to 
the edge of the leaf, thus forming elongated streaks. The leaf 
veins also become browned for some distance beyond the spots, 
although the remainder of the leaf is a normal green. The spots 
present a gray salt-and-pepper aspect, due to the whitened epider- 
mis over which the black conidial pustules are thickly scattered. 
The whitened appearance is due also to the disappearance of the 
contents of the epidermal cells and from the cells of the palisade 
layer immediately beneath them. This disappearance of cell con- 
tents is much more pronounced than in the Gnomonia ulmea spot. 

The acervuli are very numerous in a single spot and are quite 
commonly confluent. They are orbicular to oblong in shape, 
very irregular in outline, and are covered by the darkened cuticle 



i 9 2i] MILES— LEAF SPOTS OF ELM 185 

which persists for a long time, finally cracking and breaking 
irregularly to allow the dispersal of the spores. They average 
800 fx in diameter. The hymenial layer is pseudoparenchymatous, 
composed of practically colorless cells which are almost isodia- 
metrical in shape. This layer may be even thicker than that 
described for Gloeosporium ulmeum, although it presents an entirely 
different appearance, and on account of the absence of color does 
not at all suggest a stromatic base. The layer appears even 
thicker than it really is on account of the absence of all color from 
the epidermal cells, which have become entirely filled with small 
colorless crystals. This is true to a less extent of the adjacent 
layers of palisade tissue. The conidiophores are closely packed 
together, and are quite similar to those of Gloeosporium ulmeum 
except for their larger measurements, being 10-1 5X2-3 p. They 
are not as darkly colored as are those of the preceding species, 
although they are not entirely hyaline. The apex is rather blunt, 
and the conidiophore terminates rather abruptly in a sterigma- 
like projection on which the spore is borne. Occasionally two of 
these sterigma-like processes occur on a single conidiophore. The 
conidia are much larger, especially in width, and vary considerably 
in form, from oblong-cylindric to ovate, elliptical, and even pyri- 
form. They measure 8-10X3-3.5 m (fig. 17), are one-celled, 
rounded at both ends, straight, and hyaline. In no case was the 
perithecium of Gnomonia or any similar fungus found associated 
with this spot. I consider it entirely distinct from the conidial 
stage of Gnomonia ulmea, and propose for the fungus the following 
name and description. 

Gloeosporium ulmicolum, sp. nov. — Spots epiphyllous, raised, 
gray on account of the black acervuli thickly scattered over the 
whitened epidermal cells, elongated, following the leaf veins, often 
extending the entire length of the secondary veins which have 
become browned far beyond the limits of the spot; acervuli 
epiphyllous, gregarious, subcutaneous, covered by the persistent 
darkened cuticle which finally ruptures irregularly to allow the 
dispersal of the spores, averaging 800 ju in diameter, irregular in 
outline but usually elongated suborbicular; conidiophores in a 
closely packed layer, dilute-brown, cylindrical, usually nonseptate 



186 BOTANICAL GAZETTE [march 

but occasionally with a septum near the base, seated on a pseudo- 
parenchymatous hymenial base which is colorless, 10-15X2-3/*, 
terminating rather abruptly at the apex in a sterigma-like projec- 
tion on which the spores are borne; conidia hyaline, one-celled, 
straight, rounded at both ends, oblong-cylindrical, ovate, elliptical, 
or even pyriform, 8-10X3-3 .5 m- 

Habitat on living leaves of Ulmus americana. Oconomowoc, Wisconsin, 
August 22, 1919. Type specimen deposited in the herbarium of the Univer- 
sitv of Illinois. This species differs from Gloeosporium ulmeum in the shape 
and appearance of the spots, in the fact that it is not associated with a peri- 
thecial stage as that fungus constantly is, in the absence of a black basal 
stroma, and in the larger spores. In external appearance the two forms are 
quite distinct. It differs also from Gloeosporium inconspicuum Cav. and 
G. inconspicuum Cav. var. campestris Dor. in the character and appearance 
of the spot and in the much larger spores. 

Principal European leaf spot 
Systremma Ulmi (Schleich.) Thiess. and Syd.— The leaf spot of 
the elm occurring in Europe on Ulmus campestris, ■ U . ejfusa, and 
U. glabra has a somewhat superficial resemblance to that pro'- 
duced in this country by Gnomonia ulmea (Schw.) Thum. This 
may readily be seen by comparing fig. 6, which shows the European 
spot on a leaf of Ulmus campestris, with figs. 4 and 5, which are 
leaves of U. americana affected by the Gnomonia. The two diseases 
have been much confused in this country, and it has been quite 
common for American plant pathologists and mycologists to speak 
of the latter fungus under the name of the European organism. 
In examining specimens of the Gnomonia spot in various collec- 
tions in this country, I have found it quite as often referred to in 
this manner as under its true name or synonyms. There are two 
references in literature to the occurrence of the disease caused by 
Systremma Ulmi in America, in addition to various others which 
are clearly due to a confusion of the two forms. One of these 
cases is in the report by Trelease (40) of the presence in Wisconsin 
of Pkyllachora Ulmi Fuck., which name is a synonym of Sys- 
tremma Ulmi. On examination of the specimen, which is in the 
museum of the Shaw Botanical Gardens at St. Louis, Missouri, it 
was found that the disease was the American form, caused by 



i 9 2i] MILES— LEAF SPOTS OF ELM 187 

Gnomonia ulmea. Trelease also reported the presence on the 
same leaf of Septoria Ulmi Fr., a synonym of Phleospora Ulmi 
(Fr.) Wallr., which at that time was thought to be the conidial 
stage of Phyllachora Ulmi, but I was unable to find any trace of 
it on the specimen examined. In material sent from the Univer- 
sity of Geneva, Switzerland, I found another specimen, evidently 
from this same collection by Trelease and labeled in the same 
manner. It also was Gnomonia ulmea. 

The second reference to the occurrence of Systremma Ulmi in 
this country is by Ellis and Everhart (16), who stated that a 
specimen of Dothidella Ulmi (Duv.) Wint., which name is merely 
another of the numerous synonyms under which the European 
organism is known, was sent to Schweinitz by Torrey from 
New York. They added that they could not find any other 
references to this species being found in this country, and that 
they have seen no American specimens. I find in Saccardo's 
(33) Sylloge Fungorum in the description of Sphaeria apertiuscula 
Schw. on Ulmus fulva, collected by Torrey in New York, the 
statement added that the upper side of the leaf is covered with 
Dothidea Ulmi. This is evidently the specimen to which Ellis 
and Everhart were referring, as both the names used are synonyms 
of Systremma Ulmi. I have not seen this specimen, and there is 
a possibility that it is really a specimen of the European leaf spot, 
but it is hardly likely, especially since it has never been collected 
in this country since, nor has it ever been reported as occurring 
on Ulmus fulva at any other time, either previous to that collection 
or later. 

I found in specimens sent from the Royal Botanical Gardens 
at Kew, England, among those labeled as belonging to the her- 
barium of Berkeley, three specimens purporting to have been 
collected by Drummond in arctic America. These were un- 
doubtedly specimens of Systremma Ulmi, and, although the host 
was not named, the leaves possessed the somewhat three-lobed 
character peculiar to the Scotch elm, U. glabra. This is not native 
to America, and one would hardly expect to encounter an intro- 
duced species in the arctic regions. For these reasons I believe 
that these three specimens represent some European collection 



1 88 BOTANICAL GAZETTE [march 

which has in some manner accidentally become mixed with Drum- 
mond's arctic collections while they were in the process of being 
mounted at the museum. This seems all the more probable 
when it is noted that the handwriting on the labels is the same as 
that on a great many of the other specimens from the same museum. 
It would seem, therefore, quite probable that Systremma Ulmi 
does not occur at all in America. Although Ellis and Everhart 
place the causative organisms of the two diseases in the same 
genus, they express a caution against confusing the two, stating 
that although they have spores essentially the same they differ 
very markedly in other characteristics. In spite of the fact that 
the external appearances of the two spots seem quite similar to 
the casual observer, as soon as one sections them the very marked 
differences between the two fungi become apparent. Fig. 10 
represents a section through the stroma of Systremma Ulmi. It 
will be seen that the black stroma, to which the external resemblance 
between the two forms is due, is in this case subepidermal, while in 
Gnomonia ulmea it is subcuticular only. In the Systremma the 
asci are produced in locules without true perithecial walls, which 
are imbedded in the stroma and open on the upper side of the leaf, 
while in Gnomonia the perithecia, truly sphaeriaceous in character, 
are located in the leaf tissue beneath the stroma and open on the 
under side of the , leaf. Gnomonia ulmea, therefore, belongs to 
the Sphaeriales, while Systremma Ulmi belongs to an entirely 
different order, the Dothidiales. Although the asci and spores of 
the two differ but little in form, both are slightly larger in Sys- 
tremma than in Gnomonia. 

I have examined all available published exsiccati specimens of 
this fungus, as well as about 200 other specimens borrowed for 
purposes of examination and comparison from the Royal Botanical 
Gardens at Kew, and from the University of Geneva, and from a 
number of institutions and individuals in this country. The pub- 
lished exsiccati of this fungus examined were as follows: Berkeley 
Brit. Fung. no. 192; Vize Mic.-Fung. Brit. no. 277; Cooke Fung. 
Brit., Ser. I, no. 184; Briosi and Cavara Fung, paras, no. 73; 
Pollacci Fung. Longobardiae Exsic. no. 287; Saccardo Myc. Ven. 
nos. 231 and 642; Roumegere Fung. Sel. Exsic. nos. 466 and 



iQ2i] MILES— LEAF SPOTS OF ELM 189 

5761; Fl. Gall, et Germ. Exsic. no. 1000; Schleicher Crypt.Exsic. 
no. 73; Holl, Schmidt, und Kunze Deut. Schwamme no. 32; Des- 
mazieres Crypt. Fr., Ser. I, no. 284; Mongier et Nestler Stirpes 
Crypt, no. 766; von Thumen Fung. Austr. no. 499; von Thumen 
Myc. Univ. no. 2064; Fuckel Fung. Rhen. nos. 1013 and 2265; 
Sydow Myc. Mart. no. 256; Lundh. Fung. Hung. no. 374; 
Rabenhorst Herb. Myc. no. 658; Westend. Herb. Crypt, no. in; 
Krueger Fung. Sax. no. 1514; Eriksson F. Scand. nos. 292a and 
292b. 

The synonymy of the fungus is as follows: Systremma Ulmi 
(Schleich.) Thiess. and Syd., Die Dothidiales, Ann. Myc. 13:334. 
1915; Sphaeria Ulmi Schleich., Crypt. Exsic. no. 73, sec. de Can- 
dolle Fl. Franc. 2:288. 1805; Sphaeria xylomoides DC, Fl. Franc. 
2:288. 1805; Sphaeria Ulmi Duv., Hoppe's Bot. Taschenb., 105. 
1809; Xyloma sticticum Mart., Crypt. Flor Erlang., 309. 1817; 
Sphaeria ulmaria Sow., Eng. Fung., pi. 374. fig. 3; Poly stigma 
Ulmi Link, Rab. Handb. 1:167; Dothidea Ulmi Fr., Syst. 2:555. 
1823; Phyllachora Ulmi Fuck., Symb. 218; Sacc. Syll. Fung. 
2:594. 1883; Euryachora £//#«' Schroeter, Crypt. Fl. Schles. 3 2 :473- 

The conidial stage of this fungus is Piggotia asiroidea B. and Br. 

Other leaf spots of elm 

IN AMERICA 

Mycosphaerella Ulmi Kleb. (28). — This is the ascigerous 
stage of Phleospora Ulmi (Fr.) Wallr., which has been reported 
both in America and Europe as the cause of a leaf spot on Ulmus 
campestris, U. glabra, and U. americana. In the conidial stage it 
is said sometimes to do considerable damage to nursery stock and 
young trees. Stewart (36) states that it has been observed 
several times to cause extensive defoliation of young elms in New 
York. Numerous, small, reddish-brown spots appear on the upper 
side of the leaves, which in consequence gradually turn yellow, 
the margin becomes brown and rolls up, and they fall early in the 
season. The spores ooze out in minute cirrhi which dry on the 
lower side of the leaf surface and form small whitish patches. 
Saccardo (31) states that on account of the absence of pycnidia 
it leans toward Septogloeum, and it is sometimes known by that 



iqo BOTANICAL GAZETTE [march 

name. Clinton (9) and Briosi and Cavara (5) also maintain 
that it belongs to that genus and call it Septogloeum Vlmi (Fr.) 
Bri. and Cav. Clinton also suggests that Cylindrosporium ulmi- 
colum Ell. and Ev. is possibly not distinct from this species. I 
have not seen the Ellis and Everhart specimen, and admittedly 
the two descriptions are very similar, especially when one takes 
into consideration the very great differences in spore measure- 
ments recorded by various collectors of Phleospora Vlmi. Stewart 
records as follows: "As we have found them, they (the spores) 
are 3- or 4-septate, usually quite strongly curved, and measure 
34-38X5.5-6.5 ju. In no. 157 of Seymour and Earle's Economic 
Fungi, on Ulmus fulva, the spores are 3-septate, straight, and 
measure 33.5X6.3 /x. In no. 648 of Krieger's Fungi Saxonici, on 
Ulmus campestris, they are 3- or 4-septate, strongly curved, and 
measure 49.5X4.7 ju-" Under the name of Septoria Vlmi Fr., 
this fUngus was regarded by Fuckel as the spermagonial stage of 
Phyllachora Vlmi, a synonym of Systremma Vlmi, but it was shown 
by Klebahn (23) that it had no connection with that fungus, 
but was the conidial stage of Mycosphaerella Vlmi, which develops 
on the dead leaves in the spring. 

Cylindrosporium ulmicolum Ell. and Ev. — Spots becoming 
flavous; acervuli minute, hypophyllous; conidia cylindraceous, 
45-65X4 ju, hyaline, multinucleate, coming out in minute white 
caespitules. Reported on leaves of Vlmus alata in Mississippi. 
In spite of the differences in spore measurements, the possibility 
has been suggested that this is not different from Phleospora Vlmi. 

Septogloeum profusum (Ell. and Ev.) Sacc. — Spots epiphyl- 
lous, flavous; acervuli scattered, hypophyllous, large; conidia 
coming out in white cirrhi, cylindrical, oblong, granular, 3-septate, 
25-30X6-7 p. Reported on living leaves of Vlmus americana and 
V. alata, although it was first described on Corylus americana. 

Ceratophorum ulmicolum Ell. and Hark. — Causes small, 
suborbicular, dirty-brown, amphigenous spots with a white center, 
o . 5-1 cm. in diameter, on living leaves of Vlmus fulva. Noted 
from several places in the United States. 

Phyllosticta ulmicola Sacc. — Reported as being present in 
Wisconsin by Davis (13) who states as follows: 



iQ2i] MILES— LEAF SPOTS OF ELM 19 1 

Under this name I am recording the occurrence of a fungus having the 
following characteristics: Spots indefinite, immarginate, orbicular, light- 
brown, becoming cinereous above and lacerate, finally falling away in frag- 
ments, 3-7 mm. in diameter, sometimes confluent; pycnidia epiphyllous, 
scattered, black, globose to depressed, 60-80 fx; sporules globose to elliptical, 
olivaceous-hyaline, continuous, 3-6X2-3 /x. On Ulmus americana, Tisch 
Mills, August 3, 1917. Ulmus racemosa, August 5, 1917. This is probably a 
member of a group of forms of which various names have been applied in 
Europe and America. 

It has also been reported from a number of other states, among 
them Michigan, where it is said to occur on Ulmus fulva. 

Phyllosticta confertissima Ell. and Ev. — Spots red-black, 
amphigenous; pycnidia 75 ju in diameter; spores allantoid, hyaline, 
3-4X1 fi. On leaves of Ulmus fulva in Kansas. 

Phoma cincta B. and C. — Spots irregular, depressed, with a 
white border; spores oblong, narrow, 6-8 /x long. Reported on 
leaves of Ulmus americana in South Carolina. 

Excipula ulmicola Schw. — Causes widely expanded indeter- 
minate spots on the upper side of the leaf, becoming somewhat 
spotted with gray on both sides, with a broad, fuscous margin; 
pycnidia copious, immersed, excipuloid, punctiform, black, de- 
pressed in center and becoming gray. Reported as somewhat rare 
on cast-off leaves of Ulmus fulva about Bethlehem, Pennsylvania. 

Coryneum tumoricolum Peck. — Forming scattered, suborbic- 
ular, pale spots, bounded by a red -brown border on living leaves 
of Ulmus americana in the Adirondack Mountains. 

Sphaeria apertiuscula Schw. — Scattered, fuscous-black, 
minute, arising from the swollen parenchyma; at first innate, 
at length opening by a very wide mouth, but evacuate within; 
resembles a small Peziza. Recorded as occurring on the lower 
side of leaves of Ulmus fulva in New York. 

Rhytisma Ulmi Fr. — Minute, difformous, gyrose with an 
elevated margin, at length dehiscing labia tely. Reported on 
leaves of Ulmus in North America. 

Melasmia ulmicola B. and C. — Spots reddish, indefinite; 
pycnidia punctiform; spores minute, oblong-botuliform. Cook 
(10) speaks of it as the Melasmia stage of Rhytisma Ulmi, and 
reports it as very common in New Jersey. 



I 9 2 BOTANICAL GAZETTE (march 

List of species occurring in Europe only 
Acremoniella pallida Cooke and Mass., Actinonema Ulmi 
Alleschr., Ascochyta ulmella Sacc, Asteroma angulatum Desm., 
A. Fuckelii Sacc, Cladosporium hypophyllum Fuck., Exoascus 
campester Sacc, Gloeosporium incons picuum Cav., G. inconspicuum 
Cav. var. campestris Dor., Laestadia comedens (Pass.) Sacc, 
Pestalozzia maculicola Rostr., Phyllosticta bellunensis Mart., 
P. lacerans Pass., P. ulmaria Pass., P. Ulmi West., Sphaerella 
Oedema (Fr.) Fuck., S. insularis Wallr., Sphaeria ulmifolia Pass., 
Sporodesmium Ulmi Fuck., Stagonospora ulmifolia (Pass.) Sacc, 
Stigmella Castagneana (Mont.) Sacc, and Taphrina Ulmi Johans. 

Fossil leaf spots of elm 
In Meschinelli's Fungorum Fossilium Iconographia seven 
species are given occurring on leaves of fossil elms. Plates and 
figures are included for six of these, but they are very unsatisfac- 
tory in most cases, and in some instances one cannot be at all sure 
that the spot is even of fungal origin. The species are as follows: 
Sphaerites perforans Goepp., S. glomeratus (Engelh.) Mesch., 
S. rhytismoides (Ettingsh.) Mesch., Rhytismiles ulmicola (Ettingsh.) 
Mesch., R. Ulmi (Ludw.) Mesch., Depazites Ulmi (Ettingsh.) 
Mesch., and Xylomites sp. (Boulay) Mesch. 

Summary 

i. Gnomonia ulmea (Schw.) Thiim., the cause of the most 
common elm leaf spot in America, has been reported as occurring 
on five of the six native species of elm in this country and is of 
wide distribution, being found throughout the entire range of its 
hosts. Its normal host, on which it is most commonly found, is 
Ulmus americana. The fungus is not ordinarily of much economic 
importance, but may cause considerable injury to seedlings and 
young trees in nurseries by producing premature defoliation. 

2. Unlike most of the Ascomycetes, the perithecial stage of 
the fungus begins its development in the living leaf early in the 
spring. The young perithecium develops in the palisade tissue 
beneath a subcuticular black stroma. 

3. An ascogonium is found in the young perithecium, but 
there is no trichogyne. 



i92 1] MILES— LEAF SPOTS OF ELM 193 

4. An interascicular pseudoparenchyma is found present in the 
perithecium almost until the period of maturity. 

5. In the process of ascospore expulsion an entire ascus enters 
the lower part of the ostiolar canal, and the eight spores are appar- 
ently discharged simultaneously. 

6. The ascospores could not be made to germinate either in 
tap or distilled water, in nutrient solutions, on solid media, or on 
the living leaves of the English or Scotch elm. They germinated 
readily on the leaves of the American elm, however, thus indicat- 
ing that they require a special stimulus of some sort which is 
present in the leaves of some species of Ulmus, but absent in 
others. 

7. The fungus matures most rapidly during the winter on 
leaves which are neither too exposed nor in too damp a situation. 
When immersed in water or in intimate contact with the soil, the 
fungus dies, and only the empty husks of the perithecia remain. 

8. A conidial stage was found constantly associated with this 
ascigerous form. It is described as a new species, Gloeosporium 
ulmeum. 

9. The connection between the two forms was conclusively 
proven by inoculations. The ascospores of Gnomonia ulmea gave 
rise to spots on the leaves of Ulmus americana which were entirely 
typical of Gnomonia, and which bore the acervuli of Gloeosporium 
ulmeum. The spores of this form also readily infected the leaves 
of the American elm, and appeared even more virulent than were 
the ascospores, indicating that this form is probably the agent by 
which extensive dissemination of the fungus is assured in spring 
and early summer. 

10. A new leaf spot of the American elm, caused by Gloeo- 
sporium ulmicolum, another new species, is described. This 
species differs from the one previously described in the characters 
of the spot and in the larger size of the spores. 

n. Systremma Ulmi (Schleich.) Thiess. and Syd. causes a leaf 
spot of the European elms in Europe. Gnomonia ulmea has been 
very much confused with this fungus, and as a consequence has 
gotten into the literature as occurring in this country. The 
probability is, however, that it does not occur in America at all 



194 BOTANICAL GAZETTE [march 

It is a member of the Dothidiales, while Gnomonia ulmea belongs 
to the Sphaeriales. 

12. Other species of fungi producing leaf spots on the elm are 
listed with a brief comment on each of the American forms. 

13. Seven species of fungi are listed on the leaves of fossil elms. 

State Plant Board 
Agricultural College, Miss. 

LITERATURE CITED 

1. Anderson, P. J., and Rankin, W. H., Endothia canker of chestnut. 
Cornell Univ. Agric. Exp. Sta. Bull. no. 347. 1914. 

2. Bailey, L. H., Standard Cyclopedia of Horticulture. 191 7. 

3. Bachman, F. M., A new type of spermagonium and fertilization in Collema. 
Ann. Botany 26:747-760. 1912. 

4. Blackman, V. N., and Wellsford, E. J., The development of the peri- 
thecium of Polystigma rubrum DC. Ann. Botany 26:761. 1912. 

5. Briosi, G., and Cavara, F., I funghi parassiti delle piante coltivate od 
utile essicati delineati e descritti, no. 98. 1890. 

6. Brooks, F. T. , Development of Gnomonia erythrostronia Pers. Ann. Botany 
24:585. 1910. 

7. Brown, H. B., Studies in the development of Xylaria. Ann. Mycol. 
11:1-13. 1913- 

8. Clinton, G. P., Notes on plant diseases in Connecticut. Conn. Agric. 
Exp. Sta. Rept. 1909-1910 (p. 713). 

9. , Idem (p. 727). 

10. Cook, M. T., Report of the department of plant pathology. N.J. Agric. 
Exp. Sta. Rept. "1915 (p. 370). 

11. Darbishire, O. V., Uber die Apothecienentwickelung der Flechte Physcia 
pulvernlenta (Schreb.) Nyl. Jahrb. Wiss. Bot. 34:329-345. 1900. 

12. Davis, J. ]., Notes on parasitic fungi of Wisconsin. IV. Trans. Wis. 
Acad. Sci. 19:672. 1919. 

13. , Notes on parasitic fungi of Wisconsin. VI. Trans. Wis. Acad. Sci. 

19:711. 1919. 

14. Dawson, Maria, On the biology of Poronia punctata. Ann Botany 
14:245-260. 1900. 

15. Dorogin, G., Eine Pilzkrankheit auf den Blattern von Ulmus campestris. 
Zeitschr. Pflanzenkr. 20:261-263. 1910. 

16. Ellis, J. B., and Everhart, B. M., North American Pyrenomycetes. 608. 

17. Fisch, C, Beitrage zur Entwickelungsgeschichte einiger Ascomyceten. 
Bot Zeit. 40:850. 1882. 

18. Frank, B., Uber einige neue oder weniger bekannte Prlanzenkrankheiten. 
Ber. Deutsch. Bot- Gesells. 1:58. 1883. 



192 1 ] MILES— LEAF SPOTS OF ELM 1 95 

19. Fries, Elias, Syst. Myc. 2:436. 

20. Fuckel, L., Symb. Myc. 218. 

21. Gtissow, H. T., Report of botanist on plant diseases. Canada. 1910. 

22. Klebahn, H., Untersuchung uber einige Fungi Imperfecti und die zuhoeri- 
gen Ascomycetenformen. Jahrb. Wiss. Bot. 41:518. 1005. 

23. — — , Idem. Zeitschr. Pflanzenkr. 18:129-140. 1908. 

24. , Idem. Zeitschr. Pflanzenkr. 18:140-154. 1908. 

25. — , Idem. Zeitschr. Pflanzenkr. 17:223-237. 1907. 

26. — — — , Idem. Jahrb. Wiss. Bot. 41:492-518. 1905. 

27. — , Aus der Biologie der Askomyzeten. Ber. Deutsch. Bot. Gesells. 

36:47-62. 1919. 

28. Massee, G., Diseases of cultivated plants and trees, 216. 1910. 

29. Reddick, D., Black rot of grapes. Cornell Univ. Agric. Exp. Sta. Bull. 
293. 1911. 

30. Saccardo, P. A., Syll. Fung. 3:626. 1884. 
31. , Syll. Fung. 3o7§. 1884. 

32. , Syll. Fung. 1:570. 1882. 

33. , Syll. Fung. 2:440. 1883. 

34. Schweinitz, L. D. von, Syll. Fung. Carol. Sup. 55. no. 288. 

35. Stevens, F. L., Perithecia with an interascicular pseudoparenchyma. 
Box. Gaz. 68:474-476. 1919. 

36. Stewart, F. C, Notes on New York plant diseases. II. N.Y. Agric. 
Exp. Sta. Bull. 463. 1919. 

37. Stone, G. E., and Smith, R. E., Report of botanist. Mass. Agric. Exp. 
Sta. Rept. 1901, p. 57; 1902, p. 27. 

38. Thiessen, F., and Sydow, H., Die Dothidiales. Ann. Mycol. 13:325- 
1915- 

39. Thumen, F. von, Flora. 1878, p. 178. 

40. Trelease, W., Preliminary list of parasitic fungi of Wisconsin. Trans. 
Wis. Acad. Sci. 6:10. 1884. 

41. Vaughn, R. E., A method of differential staining of fungus and host cells. 
Ann. Mo. Bot. Gard. 1:241-242. 1914. 

42. Wolf, W. A., The perfect stage of Actinonema rosae. Bot. Gaz. 54:218- 
234. 1912. 

EXPLANATION OF PLATES VIII-X 

PLATE VIII 

Fig. i.— Two perithecia of Gnomonia ulmea in almost mature condition, 
showing interascicular pseudoparenchyma, and also elongated beaks and 
periphyses-lined ostiolar canal. 

Fig. 2.— Early stage in development of perithecium of Gnomonia ulmea, 
showing position in palisade layer; subcuticular stroma above has given rise 
to acervulus of imperfect form of fungus, Gloeosporium ulmeum. 



196 BOTANICAL GAZETTE [march 

Fig. 3.— Elm leaf, showing one type of Gnomonia spot; note absence of 
border of dead or browned tissue and that stromata tend to coalesce. 

Fig. 4.— Elm leaf, showing another type of spot; black stromata sur- 
rounded by border of light brown dead tissue. 

Fig. 5. — Same as fig. 4 except that epidermis covering stromata has begun 
to wear away, giving spot a lighter, somewhat ashen, appearance. 

PLA TE IX 

Fig. 6.— Leaf of English elm, showing leaf spot caused by Systremma 
Ulmi; note that each spot is but a single stroma, much more definite in out 
line than that caused by coalesced stromata of Gnomonia ulmea, and that they 
are raised much more above . surface of leaf; note also wrinkled or papillate 
appearance of stroma. 

Fig. 7. — Schweinitzian type specimen of Gnomonia ulmea. 

Fig. 8. — Perithecium of Gnomonia ulmea at earliest stage in development 
of beak and ostiole; dark portion of perithecium represents young asci just 
beginning development; note psuedoparenchymatous contents of perithecium. 

Fig. 9. — Elm leaf, showing spots caused by Gloeosporium ulmicolum, 
sp. no v.; note manner in which spots follow the veins; compare with figs. 3, 
4, 5, 7, and 12 for differences from spot caused by Gnomonia ulmea. 

Fig. 10.— Section through stroma of Systremma Ulmi, subepidermal in 
origin; note absence of perithecial walls, and that asci are borne in locules 
in stroma which open on upper side of leaf. 

Fig. 11.— Single spot, fig. 12a, enlarged 10 diameters, showing isolated 
character of stromata of Gnomonia ulmea. 

Fig. 12.— Elm leaf, showing stromata of Gnomonia ulmea as they some- 
times appear, widely separated in spot and somewhat concentrically arranged. 

Fig. 13.— Very young stage in development of perithecium of Gnomonia 
ulmea, showing pyriform shape at this stage, and connection with stroma. 

plate x 

Fig. 14.— Acervulus of conidial stage, Gloeosporium ulmeum, sp. nov., 
formed above young perithecium of ascigerous stage, Gnomonia ulmea. 

Fig. 15.— Spores of Gloeosporium ulmeum. 

Fig. 16.— Very young stage in development of Gnomonia ulmea: a, sheath- 
ing hypha; b, ascogonium; c, "suspensor" or "infection thread"; d, vegeta- 
tive hyphae which break through stroma to outer surface. 

Fig. 17.— Spores of Gloeosporium ulmicolum. 

Fig. 18. — Single acervulus of Gloeosporium stage of Gnomonia ulmea, 
showing manner of cracking to allow dispersal of spores; hyphae about acer- 
vulus are those of basal stroma as viewed from above. 

Fig. iq. — Ascus and ascospores of Gnomonia ulmea. 

Fig. 20. — Germinating spores of Gnomonia ulmea. 



BOTANICAL GAZETTE, LXXI 



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VITA 

The writer was born in Parke County, Indiana, September 25, 1890. He 
received his early education in the schools of that county, and graduated from 
Rockville High School in 19 10. He then attended Wabash College, at 
Crawfordsville, Indiana, and graduated from that institution with the degree 
of A.B. in 1914. While in his third year at Wabash, in 1913, he was elected 
to Phi Beta Kappa. 

In the fall of 1914 he accepted a position of Plant Physiological Assistant 
in Floriculture in the Illinois Agricultural Experiment Station, and registered 
in the Graduate School of the University of Illinois. In 1915 he was appointed 
Assistant in Botany in the University of Illinois, which position he retained 
until February of 191 8, when he resigned for the purpose of entering the 
military service. In the fall of 1919 he was granted a Fellowship in Botany 
in the same University. He was elected to the University of Illinois chapter 
of Sigma Xi in 191 7. 

During the summers of 191 7, 191 8, and 1919 he was employed by the 
Bureau of Plant Industry as Field Assistant in White Pine Blister Rust 
Eradication. 

His publications are: "Some Diseases of Economic Plants in Porto Rico," 
Phytopaih., VII (191 7), 345-51. "Some New Porto Rican Fungi," Trans. III. 
Acad. Sci., X (191 7), 249-55. 



